Specific anecdote:
I've been acquiring a new language over the past year or so. I went from beginner to a decent (for my purposes) level of fluency in about a year. The other day we had a friend we hadn't seen in a while over for dinner. She's a school teacher in the very language I had been learning, so, naturally, the bulk of the dinner conversation between us proceeded in that language. And, naturally, she commented on my rapid progress, when most her students can't read a comic book after eight years of study, and wanted to know more about my study technique.
I kept it positive because I didn't want to trash her whole career, but I can say that my only real secret sauce was that I studiously avoided just about every practice in mainstream language education. I didn't do what schools do, and I didn't do what Duolingo and Rosetta Stone do. Because, at the start, I spent a while reading up on the academic research on how people learn new languages. There's a lot of it, it's about as well established as any sub-field of psychology can be, and it is, to a remarkable degree, summarily ignored. The mainstream has no choice but to ignore it, because most of what's been discovered does not lend itself well to the establishment of standardized curricula or easy, objective assessment criteria. That means schools don't want to take that advice because it's incompatible with their mandate to assign letter grades, and Duolingo doesn't want to take that advice because it's impossible to gamify.